Field of the Invention
The present invention relates to a voltage regulator, and particularly to a voltage regulator equipped with an overcurrent protection circuit.
Background Art
As an overcurrent protection circuit of a voltage regulator, there are known an overcurrent protection circuit (drooping type overcurrent protection circuit) in which an output current-voltage characteristic becomes a drooping characteristic, and an overcurrent protection circuit (fold-back type overcurrent protection circuit) in which an output current-voltage characteristic becomes a fold-back characteristic.
The drooping type overcurrent protection circuit limits a current flowing through an output transistor of a voltage regulator so as not to exceed a predetermined current as illustrated in, for example, Patent Document 1. Since the limited current (hereinafter also called a “limited current”) which flows through the output transistor varies due to a manufacturing process, a resistor which receives a current made to flow by a sense transistor sensing an output current, is comprised of a plurality of resistive elements. This resistor is trimmed to thereby adjust its resistance value and set the limited current to a desired value.
On the other hand, the fold-back type overcurrent protection circuit is a circuit for preventing breakage of an IC due to an excessive loss generated when an output terminal of a voltage regulator is short-circuited to a ground terminal. As illustrated in Patent Document 2, for example, when a current of a certain value or more flows through an output transistor of the voltage regulator, current limiting is started to positively reduce an output current with lowering of an output voltage of the output transistor. Incidentally, the current flowing through the output transistor when the output terminal is short-circuited to the ground terminal is referred to as a “short-circuited current”. Even in the fold-back type overcurrent protection circuit as with the above-described drooping type overcurrent protection circuit, a resistor which receives a current made to flow by a sense transistor is comprised of a plurality of resistive elements. This resistor is trimmed to thereby adjust its resistance value and set the short-circuited current to a desired value.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2003-29856
[Patent Document 2] Japanese Patent Publication No. Hei 7 (1995)-74976